The present invention relates to a device for fixing a shoe to a bicycle pedal.
It is known that cyclists need to stably fix their feet to the pedals, especially in competition, in order to be able to apply the driving action in the best way.
Conventional toe clips with straps are currently being superseded by fixing devices which can be coupled and released without manual intervention.
This is done in order to make coupling, but especially release, easier and quicker, and to avoid the danger of falls in those cases in which it is necessary to place one foot on the ground in a very short time.
Fixing devices with automatic coupling and release also have the advantage that they do not act on the upper part of the foot, as occurred in toe clips with straps, but act on the sole instead, and that they do not limit the conditions of comfort of the foot in the shoe.
Among fixing devices with automatic coupling and release, one type comprises a plate, to be fixed to the sole of the shoe, which is provided, at the front and at the rear, with engagement wings for coupling means which are associated with the pedal.
Said coupling means are constituted respectively by a front fixed coupling element and by a rear movable coupling element which is pushed forward by a spring.
Coupling occurs by inserting the front wing in the fixed coupling and by then pressing the rear wing downward onto the movable coupling element, which is conveniently provided with a chamfer which is suitable to constitute an inclined plane which divides the pressure into two components, one of which is in a backward direction and causes snap-together coupling by contrasting the action of elastic means.
The parts are shaped so that a rotation of the plate about its position causes the backward movement of the movable coupling element and its lateral disengagement from the pedal.
However, this type of device is affected by a problem which is due to the fact that the rear movable coupling element is in practice constituted by a lever on which the elastic means are located between the fulcrum point and the anchoring point.
This entails that a considerable effort is necessary in order to produce such a counter-thrust component as to allow coupling.
Other problems are due to the fact that the foot, during pedaling, does not arrange itself flat, i.e. parallel to the ground, but it is raised in the heel region by approximately 4-5 centimeters.
Currently commercially available automatic pedals are flat.
In order to compensate for the difference in level between the foot during pedaling and the flat pedal, shoe manufacturers must produce soles which are thicker in the heel region.
This entails a further increase in weight and in the spacing of the foot from the resting point on the pedal, with a resultant loss of sensitivity during pushing.
It should be furthermore noted that automatic fixing devices are currently manufactured for pedals which are particularly suitable for road bicycles, for which the need to remove the foot from the pedal occurs rather infrequently.
For bicycles which are used in particular on rough terrain, such as those for cross-country riding or mountain bikes, there is a series of requirements which current pedals and couplings have so far failed to meet.
In particular, first of all, the pedal must be stably fixed to the shoe during pedaling; secondly, due to the fact that the feet must be frequently removed from the pedal, when recoupling occurs said pedal must be in an optimum position for rapid fixing, which must in any case be performed without the aid of the hands.